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In this paper, a superconducting gravity gradiometer system that is designed to measure full-tensor gravity gradients based on levitation-type component accelerometers without using mechanical springs is presented. All components of the gradiometer system are made of a superconducting material, niobium. Working principles are the flux quantization and the perfect diamagnetism of the superconductor. Each component of the gravity gradient tensor is obtained from the differential gravity measured by using two accelerometers, each of which is composed of a cubic test mass, a flat sensing coil, and a flat counter coil to balance the repulsive force of the sensing coil and ambient gravity. The measured signals are amplified by using superconducting quantum interference devices. The full-tensor gradiometer system consists of three perpendicularly aligned sets of gradiometers, each of which measures one diagonal and two off-diagonal components. The details of the structure of the system, the dynamics of the gradiometer, the transfer function, the common mode rejection, and the optimum conditions are discussed.

We have fabricated YBa2Cu3O7 (YBCO) dc SQUIDs containing nanobridges across twin boundaries of LaAlO3 (LAO) substrates as Josephson elements by using a focused ion beam (FIB) etching method and measured their transport properties. The beam energy was 30 keV and the current was 1.5 pA for the nanobridge pattern. Each bridge with a nominal width of 200 nm crossed a twin boundary in the (100) direction. The SQUID loop had a 10 μm × 10 μm hole with a 5.7 μm average linewidth. The SQUID voltage showed modulations in response to the external flux with a maximum modulation depth of 350 μV at 77.0 K. HR-XRD spectra showed that the epitaxially grown YBCO film was twinned in commensurate with the twinning of the LAO substrate. Tilting of the c-axis of YBCO across the twin boundary is believed to play a role as a tunnel barrier.

Using dynamic cantilever magnetometry and experimentally determining the cantilever's vibrational mode shape, we precisely measured the magnetic moment of a lithographically defined micron-sized superconducting Nb ring, a key element for the previously proposed subpiconewton force standard. The magnetic moments due to individual magnetic fluxoids and a diamagnetic response were independently determined at $T=4.3$ K, with a subfemtoampere-square-meter resolution. The results show good agreement with the theoretical estimation yielded by the Brandt and Clem model within the spring constant determination accuracy.

We have fabricated FeSe nanobridges by using a focused ion beam (FIB) etching technique and studied their transport properties. FeSe films were prepatterned into microbridges by using a standard photolithography and argon-ion-milling technique and was subsequently patterned into nanobridges by using a focused Ga+ beam with a beam current of 9 pA to minimize damage to the film. The nominal width and length of the bridges were 300 nm and 100 nm, respectively, and the film thickness was about 1,000 nm. Our film was deposited on an Al2O3(0001) substrate by using a pulsed laser deposition technique and had a (101)-oriented tetragonal phase according to its X-ray diffraction spectrum. We have studied the current-voltage (I–V) characteristics, the temperature-dependent critical current and the normal state resistance. The as-made film exhibited an onset transition temperature (Tc) of 11.0 K and zero resistivity at 6.7 K. Argon-ion milling decreased Tc, Tc,onset = 10.0 K, and Tc0 = 6.0 K, but subsequent FIB nanobridge patterning did not affect Tc. The measured transport properties of the nanobridges showed a flux-flow behavior with thermal fluctuations with negligible pinning effect. The results are compared with those of the MgB2 counterpart with a coherence length of similar size. The details of the fabrication procedure and the measured properties are discussed.

In this paper, we fabricated a low-TC second-order superconducting quantum interference device gradiometer (SQUID) to measure magnetocardiography (MCG) in unshielded environment. The second-order gradiometer consists of the pickup coil and the SQUID. The pickup coil is formed with two single-turn coils and one double-turn coil. The three coils are connected in order of single-, double-, and single-turn coil. The coupling polarity of two single coils is opposite to the double-turn coil. The SQUID is based on double relaxation oscillation SQUID (DROS), which consists of a hysteretic signal SQUID, a reference junction, and shunted a relaxation circuit with a resistor and an inductor. The DROS has ten times larger flux-to-voltage transfer coefficient (~ 1 mV/Phi0) than that of the conventional SQUID. Therefore, DROS could be operated with a simple flux-locked loop circuit. The pickup coil and the SQUID were fabricated on the independent wafers and connected superconductively using an Nb wire. The overall size of the second-order gradiometer is 94 times 12 mm2 with a baseline of 35 mm. The average field noise was about 8 fT /radicHz at 100 Hz with the second-order gradiometer in shielded or unshielded environment. The noise level is low enough to measure MCG signals in the unshielded environment. Finally, we measure the MCG in shielded and unshielded environments by using the second-order gradiometer and compared the signal characteristics measured in both environments.

Magnetocardiograms (MCG) measured using multichannel SQUID sensors of different pickup coil configuration have different magnetic signal waveforms and field distributions. In order to compare MCG data measured using different multichannel systems and to make standard format of data, we fabricated and characterized three different MCG systems each having different structure of pickup coils. Pickup coils are integrated magnetometer, planar first-order gradiometer with baseline 4 cm, planar second-order gradiometer with baseline 5 cm. The magnetometer system measures normal component of MCG fields with 61 channels, and the two planar gradiometer systems measure tangential components of MCG fields each with 64 channels. The SQUIDs are double relaxation oscillation SQUID type fabricated using Nb/Al-oxide/Nb thin film process on Si wafers. From the measured tangential field maps, normal component waveforms and field maps were reconstructed using minimum norm estimation method. The average correlation values over one cardiac cycle between the measured B z waveforms and reconstructed B z waveforms were higher than 90% both for the first-order and second-order gradiometers, meaning that we can transform reliably the tangential measurement results to the conventional normal measurement scheme.

We have designed and fabricated a uniaxial square- loop coil system to calibrate second-order SQUID gradiometers. The coil system consists of 2 pairs of identical square loops, the first pair which is Helmholtz coils for generation of uniform fields and the second pair for the 2nd-order gradient only in combination with the first pair. We obtained analytical expressions up to the 4th-order of the fields in the midplane and along the coil axis. The coefficient of the normalized second-order field term is calculated to be c(5 - 11gamma2 - 18gamma4 - 6gamma6)/(2 + 3gamma2 + gamma4)2 near the coil center, where c is -1 for the fields along the coil axis and +1/2 for those in the midplane, where gamma is the ratio of the inter-coil distance to the side length of the coil. The Helmholtz condition of a coil pair is gamma = 0.5445. The pure second-order gradient field is generated by subtracting the Helmholtz field from the field of a coil pair off the Helmholtz condition with equal magnitudes of the center fields of the two pairs. The coil system is useful for evaluating second- order SQUID gradiometers.

We have fabricated a 30 mm long baseline 2nd-order SQUID gradiometer from a single-layer YBa2Cu3O7 film. The gradiometer was patterned from a YBa2Cu3O7 film on a sapphire substrate by argon ion milling with a photoresist mask. The device had an overall size of 70.2 mm times 10.6 mm and a baseline of 30 mm with three parallel-aligned 10.2 mm times 10.2 mm pickup loops coupled directly to a dc SQUID to measure part2Bz/partx2. Josephson elements of the device were YBa2Cu3O7 nanobridges which were made by a focused ion beam technique. Design of the gradiometer was based on the same rules as those of 2.9 mm short baseline gradiometers. Gradient sensitivity of the gradiometer was estimated to be ~ 1.8 times 10-10 T/m2 /Hz1/2, which was equivalent to a field noise of 160 fT/Hz1/2, for an intrinsic SQUID flux noise of 10-5Phi0/Hz1/2. We also studied the transition properties of the YBa2Cu3O7 nanobridge. The bridge showed an superconductor- normal metal-superconductor (SNS) behavior with the top Au layer intact and an superconductor-insulator-superconductor (SIS) behavior with Au removed. We believe that the Josephson nature of the bridge is ascribed to naturally formed grain boundaries in the bridge.

We fabricated multichannel magnetocardiogram (MCG) systems of 1 magnetometer type and 2 planar gradiometer types, and compared the MCG data measured using different pickup coil systems. The magnetometer type is a 61-channel magnetometer system measuring vertical component of MCG fields. The magnetometers were integrated magnetometer structure with the pickup coil and SQUID fabricated on the same wafer. The two planar gradiometer systems are 64-channel planar gradiometer systems of first-order with a baseline of 4 cm, and of second-order with a baseline of 5 cm. The planar gradiometer systems are measuring field components tangential to the chest surface. The MCG waveforms and field distributions were measured on the same subject using the 3 MCG systems of different pickup coil types. The measured field distributions and waveforms were transformed into data of other pickup coil types, and the comparison between the measured and transformed results were done.

We have developed a new type of magnetocardiograph (MCG) system employing 6 high-TC SQUID magnetometers. We have fabricated high performance YBCO SQUID devices for the system. The lightweight MCG system, requiring liquid nitrogen as a coolant, consists of 6-channel SQUID sensors and an adjustable patient bed with sliding motion. The MCG system showed stable operation in a room with moderate magnetic shielding. In normal operation with a moving subject, we could obtain 36-point and 48-point MCG mappings with high enough signal qualities for clinical trials.

We report on the fabrication and electrical transport properties of gate-tunable superconducting quantum interference devices (SQUIDs), made of semiconducting PbS nanowire contacted with PbIn superconducting electrodes. Applied with a magnetic field perpendicular to the plane of the nano-hybrid SQUID, periodic oscillations of the critical current due to the flux quantization in SQUID are observed up to T = 4.0 K. Nonsinusoidal current-phase relationship is obtained as a function of temperature and gate voltage, which is consistent with a short and diffusive junction model., Comment: 14 pages, 4 figures

We have studied fabrication of second-order SQUID gradiometers from single-layer of high-Tc. film. The gradiometer contains three parallel-connected pickup coils which are directly coupled to a step-edge junction SQUID. In the study of short-baseline devices, we achieved an unshielded noise of 0.84 pT/cm2/Hz½ at 1 Hz for a well-balanced gradiometer. As Josephson elements of lone-baseline devices we made submicron YBCO bridges by using a focused ion beam method. In temperature-dependent critical currents, Ic(T), and normal state resistances, RN(T), the bridge showed an SIS-type behavior, which is believed to be due to naturally formed grain boundaries crossing the bridges.

We have studied noise properties and magnetocardiographic performance of single-layer second-order YBCO SQUID gradiometers made on STO substrates. A three-loop pickup coil is directly coupled to a step-edge junction SQUID with the coupling polarity of the center loop opposite to that of two side loops. Optimized device parameters for balancing were obtained from 8.8 mm /spl times/ 3.0 mm devices on 10 mm /spl times/ 10 mm substrates and scaled up to the larger devices for use in cardiomagnetic measurements. A 17.6 mm /spl times/ 6 mm gradiometer with a 5.8 mm baseline showed an unshielded gradient noise of 0.84 pT/cm/sup 2//Hz/sup 1/2/ at 1 Hz, which corresponds to an equivalent field noise of 280 fT/Hz/sup 1/2/. A large balancing factor of 10/sup 3/ allowed us to record magnetocardiogram of a human subject.

We developed multichannel SQUID magnetometer and gradiometer systems based on double relaxation oscillation SQUIDs (DROS) for use in biomagnetic studies, such as magnetoencephalogram (MEG). DROS consists of two SQUIDs (signal SQUID and reference SQUID) in series, and a relaxation circuit of an inductor and a resistor. Specially, we used single reference junction instead of the reference SQUID. Since DROS magnetometer has about 10 times lager flux-to-voltage transfer coefficient than dc SQUID, we can use simple flux-locked loop electronics for SQUID operation. The measured noise at 100 Hz was 3 fT/ √Hz for the magnetometer and 4 fT/ √Hz for the planar gradiometer, which are low enough for neuromagnetic measurements. We also constructed two kinds of multichannel SQUID systems, 40-channel and 37-channel system. Using this system, we measured several MEG signals.

We constructed a multichannel superconducting quantum interference device (SQUID) magnetometer system for magnetoencephalogram measurements. The SQUID is based on the double relaxation oscillation SQUID (DROS), which consists of a hysteretic signal SQUID and a reference junction, and shunted by a relaxation circuit of a resistor and an inductor. With the high flux-to-voltage transfers, usually larger than 1 mV//spl Phi//sub 0/, simple flux-locked loop circuits could be used for SQUID operation. The SQUID system consists of 37 integrated magnetometers, distributed on a hemispherical surface, and external feedback scheme was used to eliminate magnetic coupling with the adjacent channels. In addition to the 37 signal channels, 8 reference channels were installed to pickup background noise and to apply software gradiometer. The average noise level of the magnetometers is about 3 fT//spl radic/Hz at 100 Hz, operated inside a magnetically shielded room. The magnetometer system was applied to measure auditory-evoked fields.

We developed a transverse second-order SQUID gradiometer from a single layer of high T/sub c/ film, which can measure the off-diagonal element d/sup 2/B/sub z//dxdy of the second-order field gradient. In this design, four-way 'clover-leaf' pick-up loops are coupled directly to a 4-junction dc SQUID in such a way that the coupling polarity of the two diagonal loops is opposite to that of the other two loops. The pickup loops are intrinsically balanced for both uniform field and the 1st-order gradient. We made the device by using a pulsed-laser deposition and Ar ion-milling with photolithography. The entire structure was made on a single crystalline SrTiO/sub 3/ substrate. The gradiometer responded sensitively to the 2nd-order gradient. Induced field focused on the SQUID loop by the screening current flowing along the device perimeter is believed the major off-balancing factor, which can be balanced by adding a closed superconducting loop just outside the device perimeter or merging facing sides of neighboring loops.

We have studied detailed balancing of the directly coupled second-order YBa 2 Cu 3 O 7 superconducting quantum interference device gradiometer by adjusting the line width of the center pickup loop with all other parameters fixed. We obtained a balancing factor of 1.7×10 3 for the best-balanced device. Measured gradient noise level was 2 pT/cm 2 /√Hz at 10 Hz and the corresponding field noise was 200 fT/√Hz.

The effect of annealing step-edges on SrTiO/sub 3/ and MgO single-crystal substrates on Josephson junctions of YBa/sub 2/Cu/sub 3/O/sub 7/, has been studied. The step-edge was fabricated by argon-ion milling technique and was annealed at 1050/spl deg/C in oxygen atmosphere. YBa/sub 2/Cu/sub 3/O/sub 7/ thin film was deposited on the annealed step-edge by a standard pulsed laser deposition. The effect of annealing the step-edge on the junction was characterized by AFM and current-voltage (I-V)characteristic. The annealed step-edge on SrTiO/sub 3/ and MgO substrates showed that the surface of the substrates was smoother and I-V characteristic of Josephson junction improved.

Fine structure of isolated Mn 2+ ions in CdMnSe/ZnSe quantum wells (QWs) is revealed by optically detected magnetic resonance (ODMR) recorded by monitoring both exciton emission and intra-Mn luminescence in the presence of simultaneous microwave irradiation. A large decrease of photoluminescence (PL) intensity of excitons and an increase of PL intensity of Mn 2+ ions is observed when an applied magnetic field satisfies the Mn 2+ electron paramagnetic resonance (EPR) condition. This suggests that a spin-dependent energy transfer from excitons to intra-Mn excitations occurs at the EPR condition.

We developed a new design of the planar-type single-layer second-order SQUID gradiometer. The device consisted of 3 parallel-connected pickup loops, each of which is directly coupled to the step-edge junction dc SQUID. The device was made from a single layer of YBa/sub 2/Cu/sub 3/O/sub 7/ film patterned by photolithography with ion milling technique. Response of the device to various field distributions was tested, with 3 identical wire-wound coils coupled to each loop. Balancing was achieved by using a small piece of superconductor placed in the center loop. The gradiometer responded sensitively to the second-order field gradient, but did not respond to a uniform field or the first-order gradient. Measured off-balance was about 0.6% for the uniform field and 1.4% for the first order gradient.

We have characterized bi-crystal grain boundary junctions with various tilt angles, i.e., 24/spl deg/, 30/spl deg/, 36.8/spl deg/, and 45/spl deg/ for digital applications. A simple rapid single-flux-quantum (RSFQ) logic circuit has been fabricated using a single layer high-T/sub c/ superconducting YBa/sub 2/Cu/sub 3/O/sub 7-x/ (YBCO) thin film structure with 4 bi-crystal grain boundary Josephson junctions. The circuit includes one readout superconducting quantum interference devices (SQUID) and one storage SQUID. We have focussed upon the readout SQUID properties, including J/sub c/, R/sub n/A, and I/sub c/R/sub n/, as a function of the tilt angles of the grain boundary junctions. The 24/spl deg/-tilt grain boundary junctions were the best candidates for the simple digital circuits among the bi-crystal grain boundary junctions of the tilt angle from 24/spl deg/ through 45/spl deg/. The response of the readout SQUID was demonstrated by an input signal through the storage SQUID at 82 K.

We have designed and fabricated a square-loop Helmholtz coil system to balance and calibrate a second-order SQUID gradiometer, and measured the field distribution in the midplane. It consists of two pairs of identical square loops, one for generating uniform fields, which is a Helmholtz coil pair, and the other for generating the second-order field gradient by subtracting the Helmholtz coils’ field with equal magnitude at the center. We obtained analytical expressions in power series up to the fourth-order of the fields in the midplane and along the coil axis, and measured the field distributions for both Helmholtz and second-order gradient modes.

SQUID magnetometers have been fabricated from series arrays of YBa/sub 2/Cu/sub 3/O/sub 7/ dc SQUIDs by pulsed laser film deposition and ion mill patterning techniques. The array was designed either in linear chain with flux focusers or in meander structure. The arrays consisted of 50-130 step-edge junction SQUIDs and each SQUID had inductance of 20-40 pH with 2-5 /spl mu/m junction width. A linear array of 50 SQUIDs showed a modulation amplitude of 150 /spl mu/V which corresponds to a gain of /spl sim/10. One of 80 SQUID meander arrays had a gain of as high as 50. These results provide feasibility of the series array of SQUIDs in the direct readout SQUID amplifier circuitry with wide bandwidth. Larger number SQUID arrays and processes to increase the gain to the theoretical value need to be studied.

We have fabricated single-layer, second-order high Tc superconducting quantum interference device (SQUID) gradiometers on SrTiO3 substrates and investigated their noise properties and performance in magnetocardiography. The gradiometer consists of three parallel pickup loops that are directly coupled to a step-edge junction SQUID, in such a way that the coupling polarity of two side loops is opposite to that of the center loop. The overall size of the device is 17.6 mm×6 mm with a baseline of 5.8 mm. The measured gradient noises are 0.45 and 0.84 pT/cm2/√Hz at 1 Hz for the shielded and the unshielded cases, respectively, which correspond to equivalent field noises of 150 and 280 fT/√Hz, respectively. In spite of the short baseline of 5.8 mm, the high common-mode rejection ratio of the gradiometer, 103, allowed us to record a magnetocardiogram of a human subject, which demonstrates the feasibility of the design in biomagnetic studies.

Superconductor-normal-superconductor (SNS) step-edge junction dc SQUIDs were fabricated from YBa/sub 2/Cu/sub 3/O/sub 7/ (YBCO) films with CaRuO/sub 3/ (CRO) on top as the normal metal. The films were made by pulsed laser deposition (PLD) and patterned by photolithography and ion milling. The junctions and SQUIDs had to be annealed in oxygen environment for a much longer period of time (5-48 hours) compared with standard YBCO film preparation (as deposited or 1 hour), indicating that the top CRO film blocks oxygen in and out of the YBCO film. Before annealing T/sub c/'s of CRO/YBCO double layers and junctions made from them were 88 K and >77 K, respectively after long time annealing. Current-voltage curves of the junctions showed well-behaved resistively-shunted-junction (RSJ) properties and the temperature dependence of the junction critical current was roughly linear. SQUIDs made of those junctions showed voltage modulation in response to applied fields at 77 K. >

DC SQUID magnetometers with a directly coupled square pick-up loop have been made from single layer YBa/sub 2/Cu/sub 3/O/sub 7-/spl delta// thin films using step edge junctions or bicrystal grain boundary junctions on SrTiO/sub 3/ substrates. YBa/sub 2/Cu/sub 3/O/sub 7-/spl delta// thin films were deposited by off-axis RF sputtering or laser ablation and patterned by photolithography and Ar ion milling to form the SQUID, pick-up loop and modulation coil. The SQUIDs showed RSJ like current vs. voltage characteristics and voltage modulation in response to external fields at 77 K. The SQUID inductance was 55-140 pH, pick-up loop size was 47 mm/sup 2/ and the effective area of magnetometers estimated from the measured modulation period was 0.2-0.4 mm/sup 2/. The magnetic field noise was 7.4/spl times/10/sup -13/ T//spl radic/(Hz) at 10 Hz and 77 K. >

Effects of d-wave symmetry on the critical current of high Tc step-edge Josephson junctions were studied theoretically by using the concept of grain-boundary junctions, and the theory was compared with experimental results of YBa2Cu3O7 step-edge junctions on SrTiO3 (100) substrates. A step-edge junction contains two grain boundaries, and each grain boundary has both in-plane and out-of-plane misorientation angles at the same time. The critical current of the step-edge junction as a function of the in-plane misorientation angle has a periodic modulation with maxima when the step line is parallel to one of the major axes of the SrTiO3 (100) substrate. Experimental results of c-oriented YBa2Cu3O7 step-edge junctions with various in-plane misorientation angles were qualitatively in good agreement with the theory. The out-of-plane misorientation angle is formed between two grains usually with the c axes perpendicular to each other and is normally not controllable.

We have studied transition properties of YBa/sub 2/Cu/sub 3/O/sub 7/ step-edge junctions as a function of the angle of the step-line with respect to the major axes of the SrTiO/sub 3/ substrate. Substrate steps were prepared by Ar ion milling with photoresist mask, and the YBa/sub 2/Cu/sub 3/O/sub 7/ film was deposited by pulsed laser ablation and patterned by ion milling to form junctions. The critical temperature of the junctions was independent of the angle. However, the critical current of the junctions showed a modulation with the angle. A maximum was observed for the step-line oriented parallel to the major axes of the substrate and a minimum for the step-line oriented 45/spl deg/ against the axes. The modulation of the critical current is believed to be caused by the difference in the microscopic structure of the epitaxially grown YBa/sub 2/Cu/sub 3/O/sub 7/ film at the step and also symmetry of the high Tc superconductor.

We have studied hysteresis of the grain boundary YBa/sub 2/Cu/sub 3/O/sub 7/ Josephson junctions with Au film shunt capacitors. The capacitive shunt clearly developed hysteresis in the current-voltage curves of the junctions. However, the McCumber parameter /spl beta//sub c/, obtained from data was much smaller than the calculated values. The reason is believed to be due to the fact that the capacitive reactance was dominated by the kinetic inductance of the bridge and the series resistance of the Au film connecting the two capacitors structured on both sides of the electrodes. Using a superconducting capacitor built directly on the bridge will enhance the hysteresis. More study is needed on the inductive shunt in the junction.

We fabricated a quantum-dot device consisting of an individual double-wall carbon nanotube and studied its electrical transport properties at low temperatures. In the negative bias region, the gate modulation curve exhibited quasiperiodic current oscillations, attributed to the Coulomb blockade of single-electron tunneling. We observed both four- and eightfold shell filling in the Coulomb diamond structures. The observation implies an eightfold degeneracy in the single-particle energy levels, which is higher than the fourfold degeneracy of a single-wall carbon nanotube. We show that the observed eightfold shell filling is a unique characteristic of a double-wall carbon nanotube quantum-dot device.

We developed a noble design of the planar-type single-layer second-order superconducting quantum interference device (SQUID) gradiometer, and demonstrated that the gradiometer did not respond to a uniform field or the first-order gradient of the field but responded sensitively to the second-order gradient. The device consisted of three parallel-connected pickup loops, each of which is directly coupled to the step-edge junction SQUID. The entire structure was made from a single layer of YBa2Cu3O7 patterned by photolithography with ion milling technique. Response of the device to the field was tested with three identical wire-wound coils coupled to each loop and balancing was achieved by using a small piece of superconductor placed in the center loop. Measured off balance was about 0.6% for the uniform field and 1.4% for the first-order gradient, which were believed not due to intrinsic imbalance but mostly due to slight difference in alignment of the test coils.

Molecule‐carbon nanotube hybrid devices, utilizing self‐assembled monolayer (SAM) of chemically synthesized organic molecules and carbon nanotubes, were fabricated and their electrical properties were measured. Five different kinds of aromatic compounds with the length in the range of 1.4 – 2.2 nm were synthesized and used for the device fabrication. For most of the samples, the two‐probe resistance at room temperature was in the range of 20 kΩ – 5 GΩ. We have found that the presence of the SAM between the metal electrode and the carbon nanotube greatly enhances the two‐probe conductance, suggesting that the SAM might reduce the energy barrier formed at the metal‐carbon nanotube interface. For four out of the five molecules, the room temperature resistance showed no noticeable dependence on the length of the molecule.

Superconductor‐normal‐superconductor (SNS) type step‐edge junction dc SQUIDs were fabricated from YBa2Cu3O7−δ (YBCO) films with CaRuO3 as the normal metal by pulsed laser deposition and Ar+ beam patterning techniques. CaRuO3 films were grown epitaxially on YBCO and had a metallic conduction property. Current‐voltage curves of the junctions showed a resistively shunted‐junction behavior. Temperature dependence of the junction critical current was linear in agreement with the theory for junctions with the junction length shorter than twice of the normal coherence length (dN

The authors have fabricated superconductor-insulator-normal metal (SIN) tunnel junctions with c-axis-oriented YBCO thin films as the superconducting electrodes and studied the tunneling characteristics of the junctions by measuring the zero-bias junction resistance as a function of temperature and dI/dV as a function of the bias voltage. Measured junction resistance showed characteristic tunneling properties with a strong semiconducting background, which is ascribed to the imperfect tunnel barrier. dI/dV curves indicated gap structures at 27 mV and 4.5 mV, respectively, with a parabolic background. >

We have fabricated superconducting YBa2Cu3O7 (YBCO) nanobridges across twin boundaries of LaAlO3 (LAO) substrates by using focused-ion-beam etching and studied their critical transport properties. The nanobridges, nominally 150 nm in width, 100 – 120 nm in length, and 100 nm in thickness, showed Tc = 91 K with ΔTc ≅ 1 K and a high critical current density of Jc ≅ 1.5 × 107 A/cm2 at 77 K. Measured current-voltage curves of YBCO nanobridges across the substrate twin boundary showed resistively-shunted-junction characteristics near the transition with an excess current associated with flux flow. High-resolution X-ray diffraction spectra strongly indicated the possibility that the epitaxially-grown YBCO film was also twinned commensurate with twinning of the LAO substrate. Misorientation of the c-axis of YBCO at the twin boundary is believed to create weaknesses that dictate the behavior of the bridge across the twin boundary.

We have fabricated MgB2 dc SQUIDs (superconducting quantum interference devices) containing inter-grain nanobridges as Josephson elements by a focused ion beam (FIB) etching method and measured their transport properties. The entire structure including the SQUID loop was patterned only using a FIB. The beam energy was 30 kV and the current was 0.9 nA for larger structures and 34 and 1.5 pA for the nanobridge pattern. Each bridge with a nominal width of 100 nm crossed a single grain boundary in the normal direction. The SQUID loop had a 3.1 µm × 3.1 µm hole with a 2 µm average linewidth, corresponding to an inductance of 5.1 pH. The nanobridges had a two-step transition with an increase in the resistivity of more than a decade and a substantial decrease in the critical current density. Current–voltage characteristics showed a resistively shunted junction behavior at all temperatures below Tc, which implies that the current in the inter-grain nanobridges was determined mainly by the Josephson coupling. These results are believed to be due to discernible damage on the grain boundary caused by FIB irradiation, resulting in the formation of a tunneling barrier in the boundary. The SQUID voltage showed well-behaved modulations in response to the external flux with maximum modulation depths of 80 µV at 15.2 K and 130 µV at 5.9 K.

We have studied electrical transport characteristics of individual double-wall carbon nanotubes (DWNT) under high bias voltages. As the bias voltage applied to the carbon nanotubes increases, the outermost shell of the DWNTs broke down sequentially, which enabled us to determine the current-carrying capacity of each shell. The maximum current-carrying capacity per shell was about 150??A, which is well above that of any other previous reports.

The authors found experimentally that carbon nanotube field-effect transistors (CNFETs) could exhibit n-type characteristics even though their electrodes consist of a large-work-function metal such as Co. To explain their result, which is contrary to the general belief that CNFETs with large-work-function electrodes always lead to p-type characteristics, ab initio electronic structure calculation for the metal-carbon nanotube junction was performed, which showed that the Fermi level alignment at the junction could sensitively depend on microscopic structures of the metal-carbon nanotube junction. This suggests that deposition method of electrodes as well as the metal type could be utilized to obtain n-type CNFETs.

We report the YBa 2 Cu 3 O 7−x /SrTiO 3 (YBCO/STO) bilayer structure to prevent the deterioration of superconductivity of YBCO channel layer having a grain-boundary junction in superconducting field effect transistor. Two types of method were used, such as the 20 nm-thick STO capping layer and the 100 nm-thick PBa 2 Cu 3 O 7−x buffer layer deposition. Transition temperature of 50 nm-thick ultrathin YBCO channel layer on STO bi-crystal substrate deposited by these method increased to 80 K owing to the sufficient oxidation and the relaxation of film stress in YBCO channel layer.

We report the properties of hole-overdoped and underdoped YBa 2 Cu 3 O 7−x (YBCO) grain-boundary junctions (GBJ) on the 24° tilt SrTiO 3 (100) bicrystals as a function of temperature and junction width. Epitaxial thin films of YBCO, Y 0.7 Ca 0.3 Ba 2 Cu 3 O 7−y (Co-YBCO) were deposited by pulsed laser deposition, and the GBJs were fabricated by standard photolithography with argon ion-milling. We measured the I c R n products of ∼ 1.2 mV for Ca-YBCO and ∼ 0.3 mV for Co-YBCO GBJ at 27 K. Critical current densities(J c ) of the junctions were 1.4×10 3 and 3.0x10 4 A/cm 2 at 27 K for the Ca- and Co-YBCO GBJs, respectively. This is explained in terms of a weak-link behavior at the grain-boundaries in comparison with the bulk properties of the doped YBCO films.

We have fabricated YBa2Cu3O7−δ edge junction dc SQUIDs working at 77 K with 5∼10 nm thick PrBa2Cu3O7−δ layer as the junction barrier. The SQUIDs were made by the pulsed laser film deposition technique and the photolithographic patterning with Ar+ milling. The junctions made showed resistively-shunted-junction (RSJ) characteristics near Tc and the SQUID voltage modulation in response to magnetic fields was on the order of μ V and was observed up to 80 K.

Step edge junction dc SQUID has been made from single layer YBa 2 Cu 3 O x thin film. Step edge was formed on SrTiO 3 substrate by low energy Ar + milling. C-axis oriented YBa 2 Cu 3 O x thin film was deposited by off-axis rf sputtering and patterned across the step edge by photolithography and Ar + milling to form the SQUID loop. The SQUID showed periodic modulation signal responding to external magnetic field at 77 K and has the characteristics of 2I c ⋍40 μA and R n ⋍0.24 ω.

The effect of photolithographic treatments on the surface of a YBa2Cu3O7-δ thin film has been investigated by measuring the electrical contact resistance and performing X-ray photoemission spectroscopy (XPS) experiment. Water plays an important role in increasing the electrical contact resistance of the YBa2Cu3O7-δ thin film, as compared with the developer and photoresist (PR); water removes oxygen from the surface and increases the contact resistance. The chemical interaction with the PR or developer is not a key element in increasing the contact resistance. XPS spectra show that the oxygen concentration of the surface of a YBa2Cu3O7-δ thin film is reduced after the photolithographic process.